As a method of mounting a semiconductor chip to a circuit board, flip-chip mounting is increasing in response to a request for further reductions in weight, thickness and size of a package. In mounting of a flip-chip, there has been heretofore performed, for example, a method called “resin pre-setting mounting” in which an encapsulation resin is supplied in advance onto a substrate and then electrical connection is performed with a chip being pressure-bonded to a circuit on the substrate and curing of the encapsulation resin is also performed.
In this flip-chip mounting, there has been studied shift from chips with Au studs, conventionally widely used, to chips using Cu posts, excellent in electrical properties. In a substrate of a chip using a Cu post, connection to a circuit on the substrate is performed by fusion of solder provided at the tip portion of the post. At this time, in order to prevent the solder from protruding and flowing off a prescribed region on the substrate, a solder resist pattern is applied in advance to a region into which the solder is prevented from protruding, and a solder resist is not applied to a junction with the post. Thus, there has been made a manipulation so as to allow the solder to be placed on only a prescribed site. Accordingly, a boundary between the region where the solder resist is applied and the region where the solder resist is not applied is present in the form of a step on the substrate. It has been revealed that in resin pre-setting type flip-chip mounting, the presence of this step causes void generation due to trapping of entrained air when a chip and a substrate are pressed toward each other and an encapsulation resin is thereby forced to flow and spread in a gap between the chip and the substrate.
Moreover, it is necessary to heat up to a reflow temperature of the solder and the heating requires a higher temperature than a pressure-bonding step with a conventional Au stud. Therefore, there has been recognized the following problem: an encapsulation resin decreases in viscosity to have increased flowability and misalignment may occur before the resin is cured.
Various types of epoxy resin compositions for semiconductor encapsulation have been known; for example, an encapsulation resin provided with a latent thickening effect by blending a relatively small amount, i.e., 0.1 to 5 phr of acrylic polymer fine particles is disclosed in Patent Document 1. This encapsulation resin, however, is an encapsulant suited for wire bonding type IC chips and does not solve the above-described problems.